The present invention relates to ultrasonic inspection apparatus and, more particularly, to electronic circuitry for such apparatus.
The ultrasonic inspection of objects is frequently employed in the aircraft manufacturing industry to determine whether those objects have internal defects, such as voids or cracks, which are not apparent from an external inspection of the object. It is necessary to determine whether such defects exist because they could lead to an unexpected structural failure of air frame components incorporated into an aircraft.
Numerous systems are known in the prior art which provide a means to ultrasonically scan and analyze an object to determine whether structural defects exist within that object. Certain ones of such prior art systems contain two transducers: a send transducer which couples ultrasonic energy into the object and a receive transducer which detects or receives the ultrasonic energy transmitted through the object and generates a corresponding electrical signal. These prior art systems then analyze the electrical signal generated by the receive transducer to determine if defects exist within the object under test. However, such prior art systems are limited in at least two respects. First, it is difficult to detect some types of small defects within the object because the sensitivity and dynamic range of the system electronics is insufficient. Second, the prior art systems are not capable of operating at more than one ultrasonic frequency. The second limitation was not a major problem for the electronics of prior art systems since ultrasonic transducers could not satisfactorily operate at mere than one ultrasonic frequency. However, recent advances in transducer design have resulted in transducers which are capable of operating at more than one frequency. It is desirable to provide apparatus capable of operating at both high and low frequencies, because, while a low frequency is sufficient to detect defects in some types of objects, a high frequency is required to detect smaller defects and to inspect thinner objects. Therefore, it is desirable to provide an ultrasonic scanning system capable of operating at more than one ultrasonic frequency with increased sensitivity and dynamic range.